The present invention relates to a valve operating device having a stopping function for use in an internal combustion engine which controls the operation of an intake or exhaust valve according to the speed of the engine. More particularly, the invention relates to an oil pressure changeover valve which, in such a valve operating device, operates to select between a condition where oil pressure is applied from an oil pressure supplying source to an oil-pressure-operated part and a condition where the oil-pressure-operated part is opened to the atmosphere.
A conventional valve operating device of this type includes a cam shaft supported by a cylinder head and rotated in association with the crankshaft and a rocker arm which is rockably mounted on a rocker shaft supported by the cylinder head and which opens and closes an intake or exhaust valve following the rotation of a cam mounted on the cam shaft. The rocker arm has an oil-pressure-operated control mechanism which stops the operation of the intake or exhaust valve for specified operating conditions of the engine.
Such a control mechanism is shown in FIG. 1. A rocker arm assembly 3 is rockably mounted on a rocker shaft 2, which is in the form of a pipe having an oil passage 1. The rocker arm assembly 3 is composed of a first rocker arm 4 and a second rocker arm 5. The first and second rocker arms 4 and 5 are detachably engaged through a plunger pin 6. If the corresponding valve is to be activated, oil pressure is applied from an oil pressure source through the oil passage 1 to an oil pressure chamber 7 so as to force the plunger pin 6 in the second rocker arm 5 towards the first rocker arm 4 to thereby engage the first and second rocker arms 4 and 5 with each other. As a result, the second rocker arm 5 moves together with the first rocker arm 4, the latter following a cam (not shown) and thus being pivoted about the rocker shaft 2, causing the end portion of the second rocker arm 5 to operate the intake or exhaust valve 8. To deactivate the operation of the valve, the application of the oil pressure to the oil pressure chamber 7 is interrupted by a selector valve (not shown) so that the plunger pin 6 is restored, that is, the first and second rocker arms 4 and 5 are disengaged from each other. As a result, the rocking motion of the first rocker arm 4 is not transferred to the second arm 5.
Conventionally, switching between valve activated and deactivated states is conducted in accordance with a predetermined operating condition of the engine such as the engine speed. Typically, the engine speed is detected electrically and the operation of a solenoid valve is controlled thereby to switch the application of oil pressure to the oil pressure chamber 7.
The solenoid valve is typically constructed as shown in FIG. 2. A directly operated spool 102 is slidably mounted in a casing 101. The spool 102 is driven by a solenoid 103 to select one of a position (shown in FIG. 2) where a port 104 (connected to an actuator, namely, an oil-pressure-operated part) communicates with a return port 105 (connected to the oil tank) and a position where a port 106 (connected to an oil pump, namely, an oil pressure supplying source) communicates with the port 104.
Such solenoid valves have been extensively employed. For instance, such a solenoid valve is often used in the oil pressure circuit of a valve operating device of the type shown in FIG. 1.
However, such a valve operating system is disadvantageous in that it is relatively high in manufacturing cost because it requires expensive components such as the detecting device and solenoid valve, and it has a large number of components.
Instead of electrical control, mechanical control may be employed. In this case, a mechanical hydraulic changeover valve must be employed. However, such valves are inherently complex and costly and have not been used extensively.